Sonochemistry is the application of ultrasound to chemical reactions and processes. The mechanism causing sonochemical effects in liquids is the phenomenon of ultrasonic cavitation. Up to the present time, it is well known that there are many chemical reactions that essentially alter the speed and yield of finished products under the influence of ultrasonic cavitation.
There also exists a great number of chemical reactions that may only proceed under the influence of ultrasonic cavitation. Similar reactions may be accomplished in aqueous as well as non-aqueous, liquid-based media. The main requirement for the realization of similar reactions is the imposition of ultrasonic cavitation on the liquid medium.
Most of the chemical interaction occurs in the cavitation bubble collapse when there is significant compression and heating of the vapor and gas (Timothy J. Mason, “Advances in Sonochemistry”, Volume 3. 1993. 292 pp., JAI Press Inc). As the bubble accelerates through the collapse, no heat is lost through the bubble interface in the final collapse stage. Though no heat is lost with respect to the amount stored (adiabatic process), there is vigorous heat flux for a brief instant and a thin thermal boundary layer forms near the bubble interface.
Experimental results have shown that these bubbles have temperatures around 5000 K, pressures of roughly 1000 atm, and heating and cooling rates above 1010 K/s (K. S. Suslick, Science, Vol. 247, 23 Mar. 1990, pgs. 1439-1445). These high temperatures and pressures can create extreme physical and chemical conditions in otherwise cold liquids.
The following sonochemical effects can be observed in chemical reactions and processes: increase in reaction output and speed, changing of reaction pathway and increase in the reactivity of reagents or catalysts, improvement of phase transfer and activation catalysts, avoidance of catalysts and breakage of molecular bonds, improvement of particle and droplets formations and synthesis.
Common for all sonochemical reactions and processes is that, for the creation of cavitation bubbles in a liquid-based medium, the principle of application of ultrasonic oscillations on the liquid-based medium is used. The basic equipment which is used in sonochemistry appears as ultrasonic devices of various designs.
This method of conducting sonochemical reactions is sufficiently effective for processing small volumes of liquids and has found its chief application on the level of laboratory research. Transitioning to large scale volumes, however, which are used in industry, is significantly difficult and even at times impossible. This is associated with the problems which arise during the scaling up of cavitation that is produced with the aid of ultrasonic oscillations.
It is possible to avoid these shortcomings, however, by producing or improving the quality of the initiator of sonochemical reactions, cavitation bubbles, through the course of hydrodynamics. An example of using hydrodynamic cavitation for conducting sonochemical reactions is presented in the work of: Pandit A. B., Moholkar V. S., “Harness Cavitation to Improve Processing,” Chemical Engineering Progress, July 1996, pgs. 57-69.
A method disclosed in U.S. Pat. Nos. 5,937,906; 6,012,492; 6,035,897, for conducting sonochemical reactions and processes using large scale liquid medium volumes involves passing a hydrodynamic liquid flow at a velocity through a flow through channel internally containing at least one element to produce a local constriction of the hydrodynamic liquid flow. The velocity of the liquid flow in the local constriction is at least 16 m/sec. A hydrodynamic cavitation cavern is created downstream of the local constriction, thereby generating cavitation bubbles. The cavitation bubbles are shifted with the liquid flow to an outlet from the flow through channel and the static pressure of the liquid flow is increased to at least 12 psi. The cavitation bubbles are then collapsed in the elevated static pressure zone, thereby initiating the sonochemical reactions and processes.
The existing methods are not sufficient to generate significant compression energy release during bubble collapse.
The compression of the bubbles during cavitation in the disclosed patents under static pressure Pst increased in the liquid flow. Increasing static pressure of the liquid flow is a linear process and Pst cannot be higher than 0.3 P (to avoid cavitation suppression), wherein P is the static pressure before the local constriction where a hydrodynamic liquid flow is passed through a flow-through local constriction; Pst is the static pressure downstream of the local constriction. In most cases cavitation bubble collapse occurs when static pressure surrounding the bubble equals Pst=(0.05-0.1) P.
There are different approaches to account for the shockwave produced from the collapse of a cavitation bubble. An approximate relationship for the pressure peak amplitude, Pp, given by Brennan is: Pp=100 R Pin/r, where R is the maximum bubble radius, r is the distance from the bubble, and Pin is the external pressure surrounding the bubble which initiated cavitation bubble collapse (Pin=Pst). (C. E. Brennan, Cavitation and Bubble Dynamics, Oxford University: New York, 1995.)
Assuming adiabatic bubble collapse, maximum temperature inside a collapsing bubble can be calculated by:
            T      max        =                            T          0                ⁡                  (                                    P              in                                      P              v                                )                                      (                      γ            -            1                    )                /        γ              ,where T0 is the liquid temperature, Pin is the external pressure surrounding the bubble which initiated cavitation bubble collapse (Pin=Pst), γ is the ratio of specific heats of gas or vapor inside cavitation bubble before collapse, indicating how much heat is released from the gas during the adiabatic compression and Pv is the gas or vapor pressure inside cavitation bubble before collapse.
Thus, utilization of the recovering static pressure Pst in the liquid as external pressure which initiated cavitation bubble collapse cannot generate very high pressure the shockwave and temperature from cavitation bubble collapse and leads to a low intensity of sonochemical reactions and decrease the degree of heating the medium.
Accordingly, there is a continuing need for alternative methods of realizing sonochemical reactions which can provide more effective utilization of the energy of the hydrodynamic flow.
The present invention contemplates a new and improved device for conducting sonochemical reactions and processes that makes use of hydrodynamic cavitation for generation of controlled shockwave pressure and temperature conditions in liquids and carries out an ultrafine crush treatment for liquid materials, or achieves effective chemical reactions of liquid materials.